How to draw a graph like this to display the similarity between sequence? - (Jan/24/2007 )

Hi everybody :
Iwant to draw a graph like the picture in the attachment to display my data, but i don't know how to draw it ? who can help me ?
I only need different colour display different similarity gradationally .
Thanks !
Another question is i can't paste the picture in this post ??????
Thanks very much !!!
the figure also can be find at here.
http://nar.oxfordjournals.org/cgi/content-...34/12/3434/FIG2

If you know some perl, you can write a simple script using the perl GD module found here http://search.cpan.org/dist/GD/

Thanks!
But I am bot familar with the perl programming.
I am tring to do it by GnuPlot!
I don't know whether it is useful ?